Human recombinant beta-interferon with improved solubility

ABSTRACT

The invention relates to variants of recombinant human beta interferon and to a method for the production thereof, wherein at least one of the following amino acids Leu(5), Phe(8), Phe(15), Leu(47), Phe(50), Leu(106), Phe(111), Leu(116), Leu(120) and Phe(156) is exchanged with hydrophilic amino acid with a hydroxy group, specially serine, tyrosine or threonine, resulting in enhanced hydrophilic property of the protein surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No. 10/448,667, filed May 30, 2003, now U.S. Pat. No. 7,052,687, which is a continuation of U.S. Ser. No. 09/403,532 filed Feb. 22, 2000, now U.S. Pat. No. 6,572,853 and is the U.S. national phase of PCT/EP98/02238, filed Apr. 16, 1998. PCT/EP98/02238 claims the benefit of Federal Republic of Germany patent application serial number 197 17 864.2, filed Apr. 23, 1997. The disclosures of all of these prior applications are expressly incorporated by reference herein.

The invention pertains to variants of human recombinant beta-interferon with improved solubility.

Beta-interferon is a regulatory protein which leads to activation of genes by binding receptors. As a result, antiviral, antiproliferative and further biological activities are mediated in the cell.

The interferons, as is also the case with the interleukins, belong to the class of cytokines and are subdivided into different classes:

Type I interferon (alpha, beta, omega, tau) and Type II (gamma)

Human beta-interferon is a protein with a molecular weight of 22 kDa and 166 amino acid residues. It is formed primarily in fibroblasts during attack by a virus and possesses antiviral, antiproliferative and further biological activities. The amino acid sequence of human beta-interferon was first published by Taniguchi et al. (1980), Gene Ed. 10, pages 11 through 15, and is illustrated in SEQ ID NO: 1.

Beta-interferon, which is produced from bacterial cells or mammalian cells by genetic engineering, is being used successfully in the treatment of multiple sclerosis, a previously incurable disease in a large group of patients. However, the very high hydrophobicity of the protein, which causes very poor solubility of recombinant human beta-interferon, proves to be problematical for the production and processing of recombinant human beta-interferon.

The problem for the present invention is to make available variants of recombinant human beta-interferon whose solubility is improved in polar media, such as e.g. aqueous liquids. In addition, an objective of this invention is to indicate processes for manufacturing and possibilities for using variants of recombinant human beta-interferon with higher solubility in polar media such as aqueous liquids.

This problem is solved by the recombinant human beta-interferon in accordance with the disclosure.

In accordance with the disclosure, at least one of the following ten hydrophobic amino acids in known human beta-interferon is exchanged for a hydrophilic amino acid: Leu 5, Phe 8, Phe 15, Leu 47, Phe 50, Leu 106, Phe 111, Leu 116, Leu 120 or Phe 156. Thus the invention pertains to individual mutations as well as to all the possible combinations of these individual amino acid exchanges.

The designated amino acids are essentially located on the surface of human beta-interferon and they take up a relatively large proportion of the surface there. The exchange of these amino acids therefore leads to more than a proportionately large improvement in the hydrophilic character of the surface of recombinant human beta-interferon and it therefore increases the solubility of this protein in polar media, such as e.g. aqueous liquids. As a result of its increased hydrophilicity, the recombinant human beta-interferon in accordance with the invention is considerably simpler to handle in production as well as during its processing to give an active substance.

The production of the variants of recombinant human beta-interferon in accordance with the invention takes place in a generally known, conventional way with the help of microorganisms, e.g. in an Escherichia coli culture which has been provided with the gene for one of the proteins in accordance with the invention. The production of these microorganisms, which have been changed by means of genetic engineering, also takes place in a generally known way with the help of classical genetic engineering mutagenesis procedures for the exchange of the corresponding amino acids for hydrophilic amino acids and their synthesis will therefore be dispensed with at this juncture.

The proteins in accordance with the invention find use for the manufacture of medicinal drugs, e.g. for combatting multiple sclerosis, as well as fine chemicals for in vitro experiments or for measurements of interferon levels. The improved hydrophilicity of these proteins thereby simplifies their manufacture, transportation, storage and application in the form of a medicinal drug or fine chemical.

Advantageous further developments of the proteins in accordance with the invention are given in the dependent claims.

Exchange for the amino acids serine, tyrosine and threonine is especially advantageous and, with one hydroxy group each, these are especially hydrophilic.

As a result of its small size, serine is especially suitable for exchange since especially slight steric changes in the protein are associated with it.

The amino acid sequence of native recombinant human beta-interferon, in which the above-mentioned ten amino acids are electively exchanged for serine, is illustrated in SEQ ID NO: 2. These exchangeable amino acids are represented by Xaa. If these amino acids are exchanged, then the hydrophilicity of the surface of recombinant human beta-interferon is very much improved whereas only slight impairment arises in terms of the functionality and the efficacy of human recombinant beta-interferon.

An especially advantageous further development is illustrated in SEQ ID NO: 3 in which all of the above-mentioned ten amino acids have been exchanged here for serine so that an especially marked increase in the hydrophilicity of the surface of recombinant human beta-interferon results.

An example of a variant of human recombinant beta-interferon in accordance with the invention is given in the following sections:

FIG. 1 shows primers for the mutagenesis for the manufacture of beta-interferon in accordance with the invention.

As already described above, SEQ ID NO: 1 describes native human recombinant beta-interferon in the form in which it can already be manufactured currently with the help of known molecular biological and bio-technical possibilities.

The sequence of native human recombinant beta-interferon is illustrated in SEQ ID NO: 2 in which Xaa designates those amino acids which can be exchanged for an amino acid with at least one hydroxy group (advantageously serine, tyrosine and/or threonine) and hence result in a recombinant human beta-interferon [variant] in accordance with the invention which possesses increased surface hydrophilicity.

By way of example, all ten individual variants of beta-interferon have been manufactured in which Leu (5), Phe (8), Phe (15), Leu (47), Phe (50), Leu (106), Phe (111), Leu (116), Leu (120) or Phe (156) were exchanged for serine, whereby, in particular, the variants with exchange of the amino acids Leu (5), Phe (8), Leu (47), Phe (50), Leu (106), Phe (111), Leu (116) and Leu (120) relative to native beta-interferon, and also these variants of the Cys-17-Ser variant of human beta-interferon, excel by virtue of comparable biological activity.

SEQ ID NO: 3 shows an example of a human recombinant beta-interferon [variant] in which the following amino acids have been exchanged for serine:

Leu (5), Phe (8), Phe (15), Leu (47), Phe (50), Leu (106), Phe (111), Leu (116), Leu (120) and Phe (156). In the case of this variant of recombinant human beta-interferon, especially high hydrophilicity of the surface of the protein results and, hence, especially good solubility in aqueous solutions.

For example, the multiple variant with amino acid exchanges at positions 47, 50, 106, 111, 116 and 120 also shows activity which corresponds to the beta-interferon starting protein, with a Cys17Ser exchange, which was used in this example.

The manufacture of organisms with a gene, which has been changed in accordance with the invention, for human recombinant beta-interferon takes place by means of classical mutagenesis procedures.

Mutagenesis takes place by means of a PCR (polymerase chain reaction). The mutations are introduced via synthetic oligonucleotides. Plasmid DNA with the beta-IFN gene [translator: beta-INF gene?] serves as the template. The entire plasmid was replicated with the PCR method which was used here. The selection of the PCR fragments takes place by means of restriction digestion of the entire PCR mixture with the enzyme DpnI. This enzyme recognizes only methylated interfaces. Since fragments, which are produced in vitro by means of PCR, are unmethylated, only the template DNA is degraded by DpnI. After DpnI digestion, in the event of success, a fragment with the length of the linearized template remains behind and this carries the mutations. The PCR fragments, that are produced, are cloned and sequenced.

PCR mixture (100 ml): template DNA 10 mg primers 100 pmol each nucleotide mix 200 mM per dNTP MgSO₄ 2-6 mM DNA polymerase 2.5 units PCR protocol Duration Temperature step 1. 4 min 95 C. step 2. + enzyme step 3. 45 sec 95 C. step 4.  1 min 55 C. step 5. 10 min 68 C. goto [sic] 3. (11x) step 6. 10 min 68 C. step 7.  4 C.

The PCR was carried out in a Thermocycler PTC-200 (MJ Research company).

Two primers are necessary for each PCR, namely a “forward” primer and a “reverse” primer. The two primers follow one another directly but, in each case, they bind to different strands with the opposite orientation.

FIG. 1 illustrates primers which were used for the mutagenesis in order that the amino acid(s), that are designated on the left, be exchanged for serine in the gene product, i.e. the beta-interferon in accordance with the invention.

The last two primers alone contain “reverse” primer mutations. A PCR with these primers additionally introduces mutations without the previously inserted mutations 5/8 or 106/111 being relinquished. If the wild type is taken as a template, then four mutations can be introduced at the same time via the “reverse” primers (5-17 or, as the case may be, 106-120). 

1. A method of preparing a human beta-interferon variant comprising the step of substituting at least one of the amino acids in native human beta-interferon (SEQ ID NO: 1) selected from the group consisting of Leu (5), Phe (8), Phe (15), Leu (47), Phe (50), Leu (106), Phe (111), Leu (116), Leu (120), and Phe (156) for an amino acid with at least one hydroxy group selected from the group consisting of a serine, a tyrosine, and a threonine.
 2. The method of claim 1 wherein the human beta-interferon variant is prepared recombinantly.
 3. The method of claim 2 wherein a host cell is transformed with a nucleic acid encoding the human beta-interferon variant.
 4. Beta-interferon prepared according to the method of claim 1 comprising the amino acid sequence of SEQ ID NO:
 3. 5. Beta-interferon prepared according to the method of claim 2 comprising the amino acid sequence of SEQ ID NO:
 3. 6. Beta-interferon prepared according to the method of claim 3 comprising the amino acid sequence of SEQ ID NO:
 3. 